1. Field of the Invention
The present invention relates to a configuration of a speaker device preferably usable for a mobile phone.
2. Description of Related Art
Conventionally, there is known a Ryffel-type speaker including a rectangular diaphragm and a liner voice coil arranged at a central part of the diaphragm (see “New Edition Encyclopedia of Speakers and enclosures” Tamon Saeki, Seibundo-Shinkosha, Aug. 1, 2002, Vol. 3, P. 40, for example). The speaker having a configuration of this kind is disclosed in Japanese Patent Applications Laid-open under No. 11-187484 and No. 10-191494, which are referred to as References-1 and 2, respectively.
The speaker according to Reference-1 mainly includes two diaphragms and a magnetic circuit including two, i.e., upper and lower magnetic gaps in parallel with each other and having opposite magnetic flux directions. At substantial centers on rear surfaces of the respective diaphragms, two, i.e., upper and lower voice coils are arranged, respectively. Thereby, it is said that, even with an elongated configuration having narrow opening diameter and horizontal width, a minimum resonance frequency f0 can be low, and withstand input and a characteristic between low frequency reproduction and a sound pressure frequency can be improved.
The speaker according to Reference-2 mainly includes a rectangular diaphragm, a plate-shaped driving force transmission member connected with the diaphragm and inserted to the magnetic gap of the magnetic circuit, a damper formed into a substantially “S” shape, and a voice coil connected with a driving force transmission member. Thereby, suppression of displacement difference in an up-and-down direction, reduction of non-linear distortion at large magnitude and low frequency reproduction can be realized. The speaker includes one or two magnetic gap(s) in which the voice coil is arranged.
Supporting methods of the voice coil at a predetermined position of the diaphragm in the speaker are disclosed in Japanese Patent Publications No. 3337631 and No. 3334842, which are referred to as References-3 and 4, respectively.
The speaker according to Reference-3 includes a recessed part having a U-shaped cross-section at an outer peripheral edge portion of the diaphragm in a ring state, an edge damper at an outer peripheral edge portion of the recessed part, and a cylindrical voice coil attached to the inside of the recessed part by an adhesive. The voice coil is arranged in the magnetic gap of the magnetic circuit together with the recessed part and supported in a floating manner by the edge damper. Additionally, in the speaker according to Reference-4 the diaphragm has the voice coil arranged on an outer circumferential surface of a short cylindrical part provided at an end edge part of a main part formed into a semi-sphere shape.
However, the speaker device according to the above-mentioned References-1 and 2 structurally becomes thick in the vibration direction of the diaphragm, and there is such a problem that the speaker device is hardly applied to a recent mobile phone of a thin-type.